Disk array unit

ABSTRACT

A disk array unit connected to a host unit to give information thereto and receive information therefrom. The disk unit includes a plurality of disk units for storing information transmitted from the host unit and a management information recording device, formed by utilizing information storage areas in the disk units, for causing information relating to a logical unit for storing information from the host unit to correspond to information relating to the units. The invention further includes a control unit, when there is no access from the host unit to the logical unit for a predetermined time, for determining the disk units corresponding to the logical unit based on information recorded in the management information recording device and performing power saving of power supply for the disk units.

BACKGROUND OF THE INVENTION

The present invention relates to power saving of computer apparatuses,peripheral devices, and other electronic apparatuses, and in particularto energy saving of a disk array unit connected to a computer apparatus.

The disk array unit is a peripheral device of a computer apparatus, andis used as an external storage unit for storing data of the computer. Aplurality of magnetic disk units are mounted on the disk array unit.When the disk array unit and a computer system serving as a host unit ofthe disk array unit are functioning, all of a plurality of magnetic diskunits mounted on the disk array unit are typically operating.

In the specification of the present application, a term “operating”means that a magnetic disk unit is ready to response immediately whencontrol information or data is inputted to the magnetic disk unit from acontrol unit or a host unit. It is now assumed that the magnetic diskunit is in the so-called sleep mode and a magnetic disk medium is in thestill state. When a time required for the magnetic disk medium to bespun up to its ordinary number of revolutions has elapsed, the magneticdisk unit responds. This case is not included in the scope of the term“operating”. Furthermore, the term “operating” does not include the casewhere the magnetic disk unit is in the power saving mode and it respondsafter the power saving mode has been canceled.

Furthermore, when viewed from a magnetic disk unit, the term “access”means whether a command intended for itself has been issued or whetherinformation giving and receiving intended for itself has been requested.Typically, it corresponds to that in response to an instruction ofinformation acquisition or storage of a host unit, a signal is issuedfrom an electronic circuit of the host unit side including a driveinterface to a magnetic disk unit intended for.

When an access from a host unit has occurred, the magnetic disk unit tobe accessed must be operating so as to be capable of transmitting orreceiving control information, the magnetic disk unit to be accessedmust be operating. On the other hand, in the case where there is noaccess from a host unit or a control unit, it is not necessary to keepthe magnetic disk unit in the “operating” state.

For magnetic disk units, there is typically a control method includingthe steps of throwing the power supply upon receiving access from a hostunit, rotating a magnetic recording medium, and answering to the access(transmitting or receiving information), and gradually cutting the powersupply of predetermined electronic circuits and a motor for rotating themagnetic recording medium after the answering has been finished. Inother words, the magnetic disk unit has various power saving modesbuilt-in, and has a function of selecting a predetermined power savingmode according to mainly the frequency of access from a host unit or acontrol unit, and automatically shifting into that mode.

In a conventional disk array unit, mounted magnetic disk units ormagnetic disk units so set as to be recognizable from a host unit arecontrolled so as to become operating in response to start of the diskarray unit. After the disk array unit has been started, the abovedescribed magnetic disk units mounted thereon remain operating until thepower supply of the disk array unit is cut. If such manipulation as tocut the power supply of the disk array unit is conducted, such asequence as to shift the magnetic disk units from the “operating” stateto power supply off-state functions in response to the manipulation, andthereafter the power supply of the disk array unit is cut.

As for magnetic disk units which have not been so set as to berecognizable from a host unit and magnetic disk units mounted as spares,the power supply is thrown and a magnetic disk unit is made “operating”,when a magnetic disk unit is so set as to be recognizable from a hostunit or a magnetic disk unit for spare is used. Once a magnetic diskunit is made operating, the power supply is not cut individually untilthe power supply of the disk array unit is cut. In the case of amagnetic disk unit having an increased number of magnetic disk units,such as a disk array unit having several hundreds magnetic disk unitsconnected, therefore, a power saving measure becomes indispensable.

SUMMARY OF THE INVENTION

In a disk array unit, it is not necessary to make all magnetic diskunits operating, in the case where the number of accesses from the hostunit is not many. Therefore, it is considered that power saving ispossible by applying the above described control method. However, a timefor making a magnetic disk unit “operating” upon receiving an access isrequired, and the performance of the disk array unit as a whole issignificantly degraded. For preventing degradation of the performance,it is necessary to select and execute a power saving mode having a shortreturn time to “operating”, use a magnetic disk unit having a short timeuntil spin up, or consider access to a memory for holding data insteadof a magnetic disk unit.

Furthermore, in such a disk array unit that one set of magnetic diskunits (physical unit) is not handled as one logical unit, power savingof disk array units cannot be realized by simply diverting the existingpower saving mode of magnetic disk units.

In the case where there has been no access to one set of magnetic diskunits (physical unit group) from the host unit or control unit for apredetermined time, one of a plurality of power saving modes is selectedand the set of magnetic disk units is brought into the power savingmode. In this power saving mode, a mode for stopping the rotation of amagnetic recording medium is included.

In the case where one set of magnetic disk units (physical unit group)corresponds to two or more logical units, one of a plurality of powersaving modes is selected and the set of magnetic disk units is broughtinto the selected power saving mode, provided that there has been noaccess to all of the two or more logical units from the host unit orcontrol unit for a predetermined time.

In the case where one logical unit is defined for more than one set ofmagnetic disk units (physical unit group), one of a plurality of powersaving modes is selected and the set of magnetic disk units is broughtinto the selected power saving mode, provided that there has been noaccess to all magnetic disk units corresponding to the one logical unitfrom the host unit or control unit for a predetermined time.

In order to execute such control, there are provided a means forassociating a configuration of magnetic disk units with access from thehost unit, a power saving control means for selecting a power savingmode of magnetic disk units recognized by the disk array unit, and adiagnosis means for diagnosing the state of magnetic disk units. Herein,the term “diagnosis” means confirming the operation of a magnetic diskunit to determine whether the magnetic disk unit is in the usable state.For example, an online verify command is executed, and it is determinedwhether that command causes normal termination.

BRIEF DESCRIPTION OF THE DRAWING

FIG. 1 is an entire configuration diagram of a disk array unit accordingto an embodiment of the present invention;

FIG. 2 is a diagram showing a management table according to anembodiment of the present invention;

FIG. 3 is a magnetic disk unit power supply throwing operation flowchart according to an embodiment of the present invention;

FIG. 4 is a magnetic disk unit power supply cutting operation flow chartaccording to an embodiment of the present invention; and

FIG. 5 is a magnetic disk unit power supply diagnosis operation flowchart according to an embodiment of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

Hereafter, embodiments of a disk array unit of the present inventionwill be described.

FIG. 1 shows an example of the internal configuration of a disk arrayunit 110 connected to a host unit 101.

The host unit 101 controls information reading and writing, andimplements information reading or writing by issuing a command to thedisk array unit 110.

The disk array unit 110 includes a host interface circuit 120, a controlunit 160, a data base transfer circuit 170, a drive interface circuit180, magnetic disk units 190, a spare magnetic disk unit 191, anoperation panel 130, a LAN control unit 140, and an RS 232C control unit150.

The control unit 160 is implemented by using a microprocessor andfirmware for control. The control unit 160 includes a main control unit161 and a timing mechanism 163 for managing time. On a memory 162included in the control unit 160, various management tables arearranged.

If small sized magnetic disk units which are general purpose componentsare used as the magnetic disk units 190 and a spare magnetic disk unit191, a great effect of manufacturing cost reduction is brought about.The magnetic disk units 190 are arranged in an array form so as to forma RAID (Redundant Array Inexpensive Disks) configuration (FIG. 1).

A RAID group is formed of one column (200, 201) or a plurality ofcolumns (202). As for the magnetic disk units 190 forming a RAID group,a concept called RANK is introduced in order to make possible accessfrom the host unit 101, and a logical unit is set for each RAID groupconfiguration. In each same RANK, the storage area of each magnetic diskunit is divided (area division).

Typically in the disk array, user data, for example, is divided in dataof a suitable size (striping), distributed to magnetic disk units, andstored in them. And it is desirable for the disk array to conduct datastorage and access to its own magnetic disk units uniformly. Therefore,the concept called RANK is associated with the configuration including aplurality of logical magnetic disk units. Therefore, one set of magneticdisk units can be associated with a plurality of logical disk units orwith less than one logical disk unit.

Association of RANKs with logical units is determined by settingconfiguration information of the disk array unit 110. It is possible tolet n RANKs=one logical unit, one RANK=n logical units, or m RANKs=nlogical units. In FIG. 1, LU 0 (210, logical unit number 0) isassociated with RANK 0 (200), LU 1 (211) and LU 2 (212) are associatedwith RANK 1 (201), and LU 3 (213) and LU 4 (214) are associated withRANK n (202).

When a fault has occurred in the magnetic disk units 190 forming a RAIDgroup, the spare magnetic disk unit 191 is used as a magnetic disk unitfor substitution. To be concrete, a diagnosis is executed to detect afault, and the faulty magnetic disk unit 190 is substituted for thespare magnetic disk unit 191. In FIG. 1, only one spare magnetic diskunit is illustrated, but it is not restrictive.

FIG. 2 shows a structure of various management tables stored on thememory 162.

A magnetic disk unit management table 250 manages information of each ofpreset logical units. The preset logical unit is managed since itsnumber is registered in “preset LUN”. In the case of the configurationof the RANK n (202), the configuration has a plurality of columns, andconsequently “management LUN” is used and a divisional branch number isregistered therein for management. Furthermore, time when access to alogical unit from the host unit 101 has been received is registered in“access time”. The position of the magnetic disk unit 190 in the presetlogical unit is registered in “magnetic disk unit position”. In the casewhere a plurality of logical units have been preset in the same RANK asshown in RANK n (202), other logical unit numbers included in the presetplurality of logical units are registered in“relating LUN”. The timewhen the magnetic disk unit 190 has been brought into its power savingmode, or the time when the power supply of the magnetic disk unit 190has been cut is registered in “power saving start time”.

In “power saving waiting time” 260, there is registered time to elapsesince the last access from the host unit 101 was received until themagnetic disk unit 190 is brought into the power saving mode or itspower supply is cut.

In “diagnosis start time” 270, there is registered time to elapse sincea magnetic disk unit 190 was brought into the power saving mode or thelike until diagnosis of the magnetic disk unit 190 is started, or timewhen diagnosis of a magnetic disk 190 brought into the power saving modeor the like should be executed.

Hereafter, a power saving method relating to the present invention willbe described by referring to flow charts (FIGS. 3, 4 and 5).

The host unit 101 executes an application, and stores necessaryinformation in the disk array unit 110. The necessary information istaken out or written into the disk array unit by read or write access,and makes a necessary function active.

When the disk array unit 110 is started, it throws the power supply ofnecessary magnetic disk units 190 in order to be able to respond toaccess from the host unit.

As for the spare magnetic disk unit 191, typically it is not accessed bythe host unit 101. After the power supply of the spare magnetic diskunit 191 is thrown and it is confirmed that the spare magnetic disk unit191 functions normally, therefore, the power supply is cut. Instead ofcutting the power supply of the spare magnetic disk unit 191, the sparemagnetic disk unit 191 may be kept waiting in the power saving mode.

After throwing the power supply of the magnetic disk units 190 andconfirming normal operation of the magnetic disk units 190, the diskarray unit 110 conducts registration of “preset LUN”, “management LUN”,“access time (the time when the normality of the magnetic disk units isconfirmed)”, “magnetic disk unit position”, and “relating LUN” (FIG. 2).In the case where the RANK n (202) is formed of a plurality of magneticdisk units 190, information for dividing a logical unit into respectivecolumns and managing the logical unit as respective columns isregistered in the “management LUN”. The LU 4 (214) is registered in the“management LUN” as LU 4-1 and LU 4-2.

In the case where a plurality of logical units are preset in the sameRANK as indicated by RANK 1 (201), relating LUNs are registered in the“relating LUN”. In the “relating LUN” of the LU 1 (211), LU 2 (212) isregistered. In the “relating LUN” of the LU 2 (212), LU 1 (211) isregistered.

After registering such information, power supply cutting processingshown in FIG. 4 and diagnosis processing shown in FIG. 5 are started.Instead of the power supply cutting processing, processing for the shiftto the power saving mode may be conducted. In the case of the powersupply cutting processing, the effect of power saving is great.Hereafter, therefore, an embodiment will be described laying stress onthe power supply cutting processing. Instead of the power supplycutting, however, selection and execution of the power saving mode maybe conducted.

As for the “access time” and the “power saving start time” (power supplycutting time), they are registered by referring to the timing mechanism163 included in the control unit 160 for the current time.

When the disk array unit 110 has received access from the host unit 101,the power saving start time of magnetic disk units 190 belonging to alogical unit to be accessed is judged by referring to the magnetic diskunit management table 250. In the case where the power saving start timeis not registered, the access is executed in succession. In the casewhere the power saving start time is registered, the power supply of themagnetic disk unit is in the off state or in the power saving mode.Therefore, the power supply of the magnetic disk units 190 registered inthe magnetic disk unit position of the magnetic disk unit managementtable 250 is thrown or the power saving mode thereof is canceled, thepower saving start time is cleared, and then the access is executed.After the access execution has been finished, the access time is updatedto the current time.

In the power supply cutting processing shown in FIG. 4, the access timeof magnetic disk unit management table 250 is monitored by taking apreset logical unit as the unit. As for a logical unit which has ceasedto be accessed from the host unit, the time registered in the “accesstime” is compared with the current time. When the difference hasexceeded the “power saving waiting time” 260, magnetic disk units 190belonging to the subject logical unit are determined on the basis of the“magnetic disk unit position” of the magnetic disk unit management table250, and the power supply of the magnetic disk units 190 registered inthe “magnetic disk unit position” is cut or brought into the powersaving mode. The time when the power supply has been cut is registeredin the “power saving start time” (FIG. 2).

In the case where the “power saving waiting time” 260 has been exceeded,it is determined whether power supply should be thrown or cut (whetherthe mode is the power saving mode) on the basis of the state of the LU 2(212) of the registered “relating LUN”. In the case where the LU 2 (212)has not exceeded the power saving waiting time, it is judged that thepower saving start time of the magnetic disk unit management table 250is not registered and a magnetic disk unit 190 is being used in the LU 2(212). The power supply of the magnetic disk unit is not cut, or it isnot brought into the power saving mode. If the LU 2 (212) has exceededthe power saving waiting time, then the “power saving start time” of themagnetic disk unit management table 250 has already been finished inregistration, and the LU 2 (212) has exceeded the power saving waitingtime together with the LU 1 (211). Therefore, the power supply of themagnetic disk units 190 in the “magnetic disk unit position” is cut. Thetime when the power supply has been cut is registered in the “powersaving start time”.

In the case where the “power saving waiting time” 260 is exceeded forthe LU 4 (214), it is determined whether the power supply should be cuton the basis of the “management LUN” in which the LU 4 (214) isregistered. The LU 4 (214) is one logical unit configuration, but it isformed of a plurality of columns of magnetic disk units 190. Therefore,the LU 4 (214) is divisionally managed in the “management LUN”. A firstcolumn is registered as LU 4-1, and a second column is registered as LU4-2. As for the LU 4-1, the LU 3 (213) is registered in its “relatingLUN”. In the case where the “power saving start time” of the LU 3 (213)is not registered, therefore, the power supply of the magnetic diskunits 190 of the first column is not cut, because the magnetic diskunits are used in the LU 3 (213). As for the LU 4-2, there are norelating LUs, and consequently the power supply of magnetic disk units190 of the second column is cut. The time when the power supply has beencut is registered in the “power saving start time”. In this way, in theLU 4, it is made possible to cut the power supply of a part of a groupof magnetic disk units forming one logical unit or shift the powersupply of the part of the group into the power saving mode.

In the diagnosis processing of FIG. 5, the “power saving start time” ofthe magnetic disk management table 250 is monitored by taking a presetlogical unit as the unit. The time registered in the “power saving starttime” is compared with the current time. When the difference hasexceeded the “diagnosis start time” 270, magnetic disk units 190belonging to the subject logical unit are determined from the “magneticdisk unit position” of the magnetic disk unit management table 250, anddiagnosis of the magnetic disk units 190 registered in the “magneticdisk unit position” is executed. After the diagnosis has been finished,the power saving mode is started.

In the case where a diagnosis is executed, access processing from thehost unit 101 is given priority. When access has been received, thediagnosis is stopped and access is executed. After the access processinghas been finished, the diagnosis is resumed.

As for the diagnosis of the magnetic disk units 190, time of twenty-fourhour clock is registered in the “diagnosis start time” 270. Instead ofreferring to the time elapsed since the power supply is cut, when theregistered time is reached, the diagnosis is started. Alternatively, thediagnosis may be started on the basis of the time elapsed since thepower supply is cut.

In the case where a diagnosis is executed, access processing from thehost unit 101 is given priority. When access has been received, thediagnosis is stopped and access is executed. After the access processinghas been finished, the diagnosis is resumed. Diagnoses for magnetic diskunits of a logical unit registered in the magnetic disk unit managementtable 250 are executed simultaneously by taking a logical unit as theunit. In the case where a logical unit is formed of a plurality ofcolumns, diagnosis is executed by taking, as the unit, a “managementLUN” of management conducted by taking a column as the unit. Diagnosesof as many magnetic disk units 190 as the number of magnetic disk unitsin a maximum column configuration are conducted simultaneously. In thecase of the configuration of FIG. 1, diagnoses of five magnetic unitsincluding two magnetic disk units which are not illustrated areconducted simultaneously in each RANK. In the case where, for example,four magnetic disk units are mounted on one RANK, diagnoses of the fourmagnetic disk units are conducted simultaneously. This aims at checkinglogical magnetic disk units functioning as a disk array of that RANKbefore use.

Although it is a special embodiment, the present invention can also beapplied to a disk array having only one magnetic disk unit in one RANK.In this case, one set of magnetic disk units is formed of one magneticdisk unit.

Diagnosis of the spare magnetic disk unit 191 is conducted when a fixedtime has elapsed. In the case where time of twenty-four hour clock isregistered in the “diagnosis start time” 270, the diagnosis of the sparemagnetic disk unit 191 may be conducted when the registered time hasbeen reached.

The “power saving start time” 260 and the “diagnosis start time” can bealtered from the host command, operation panel 130, the LAN port 140,and the RS 232C port. When a directive of alteration has been received,information of the memory 162 is updated. Alteration according to a hostcommand is conducted by a vendor unique command directing alteration ofsuch information. Alteration using the operation panel 130 is conductedby displaying an alteration setting menu of such information and makingan operator inputting a value to be altered. Alteration using the LANport and the RS 232C port is conducted by prescribing a specificinterface, burying information to be altered into the interface, andsending information from a device to which the LAN and the RS 232C areconnected. The altered information is written into the memory 162 whenan alteration directive is given. When writing has been finished, thealtered information is made effective.

The present invention can suppress the power consumption of magneticdisk units mounted on the disk array unit. Furthermore, since thesubjects are magnetic disk units which are not accessed from the hostunit, it is made possible to save energy while preventing significantperformance degradation. Furthermore, by conducting a diagnosis onmagnetic disk units cut in the power supply, it is possible to confirmthe reliability of magnetic disk units which are often susceptible topower supply cutting.

To be more concrete, in one magnetic disk unit requiring electric powerof 20 W at the time of rotation start, its electronic circuit consumes5.5 W at the time of read/write, and consumes 3.5 W at the time ofread/write idle. A spindle of that magnetic disk unit consumes electricpower in the range of 4 to 5 W at the time of idle rotation. If in thiscase the power saving mode for stopping the function of the electroniccircuit is selected, the power consumption of at least 3.5 W isprevented. If the rotation of the spindle is also stopped, powerconsumption in the range of 4 to 5 W is prevented in addition.

Actually, power saving is conducted by taking a RANK as the unit. If theelectronic circuit of one RANK is in the power saving mode in a diskarray having a five column configuration, power consumption ofapproximately 18 W is prevented. If the rotation of the spindle is alsostopped, power consumption in the range of 20 to 25 W is prevented.According to use of the disk array unit, these numerical values increaseor decrease. For example, because of a change in access demand betweenday and night in twenty-four hour continuous running and execution timeof the power saving mode consequent thereupon, the power saving effectbecomes great.

What is claimed is:
 1. A disk array unit connected to a host unit togive information thereto and receive information therefrom, said diskarray unit comprising: a plurality of disk units for storing informationtransmitted from said host unit; a management information recordingdevice, formed by utilizing information storage areas in the pluralityof disk units, for causing information relating to a logical unit forstoring information transmitted from said host unit to correspond toinformation relating to the plurality of disk units; and a control unit,when there is no access from said host unit to said logical unit for apredetermined time, for determining said plurality of disk unitscorresponding to said logical unit based on information recorded in saidmanagement information recording device and performing power saving ofpower supply for said plurality of disk units.
 2. A disk array unitaccording to claim 1, further comprising: a timing mechanism formeasuring a time at which the access is transmitted from said host unitto said logical unit, wherein said control unit determines that there isno the access from said host unit for said predetermined time based onthe time measured by said timing mechanism.
 3. A disk array unitaccording to claim 1, wherein said control unit performs the powersaving of the power supply for said determined plurality of disk unitsby using one of a first power saving mode for suppressing powerconsumption of a part of an electronic circuit and a second power savingmode for suppressing power consumption by controlling rotation of aspindle, and wherein when there is no access from said host unit to saidlogical unit for said predetermined time, the power saving of powersupply of said determined plurality of disk units is performed by saidfirst saving power mode.
 4. A disk array unit according to claim 1,wherein said control unit performs the power saving of the power supplyfor said determined plurality of disk units by using one of a firstpower saving mode for suppressing power consumption of a part of anelectronic circuit and a second power saving mode for suppressing powerconsumption by controlling rotation of a spindle, and wherein when thereis no access from said host unit to said logical unit for saidpredetermined time, the power saving of power supply of said determinedplurality of disk units is performed by said second saving power mode.5. A disk array unit according to claim 1, further comprising: aplurality of logical units for said plurality of disk units, whereinsaid control unit performs power saving of power supply for saiddetermined plurality of disk units, when there is no access from saidhost unit to any of said plurality of logical units for saidpredetermined time.
 6. A disk array unit according to claim 5, whereinsaid management information recording device stores as informationrelating to said plurality of logical units information indicating thatthe respective logical units are composed using information storageareas of said plurality of disk units together.
 7. A disk array unitaccording to claim 5, wherein said control unit performs the powersaving of the power supply of said determined plurality of disk units byusing a power saving mode for suppressing power consumption by controlof rotation of a spindle.
 8. A disk array unit according to claim 1,wherein said logical unit is composed over information storage areas insaid plurality of disk units and information storage areas in the otherplurality of disk units, and wherein said control unit performs powersaving of the power supply of said plurality of disk units and powersupply of said other plurality of disk units, when there is no accessfrom said host unit to said logical units for said predetermined time.9. A disk array unit according to claim 8, wherein said managementinformation recording device stores as information relating to saidlogical unit information indicating that the information is composedover information storage areas in said plurality of disk units andinformation storage areas in the other plurality of disk units.
 10. Adisk array unit according to claim 8, wherein said control unit performspower saving of said plurality of disk units and said other disk unitsby using a power saving mode for suppressing power consumption bycontrol of rotation of a spindle.
 11. A disk array unit according toclaim 1, wherein said logical unit is composed over information storageareas in said plurality of disk units and information storage areas inthe other plurality of disk units, wherein said other plurality of diskunits have an information storage area for constituting another logicalunit, and wherein, when there is no the access from said host unit tosaid logical unit for said predetermined time, said control unitperforms the power saving of the power supply of said plurality of diskunits based on information recorded in said management informationrecording device, in consideration of an access time from said host unitto said other logical unit.
 12. A disk array unit according to claim 11,wherein said management information recording device stores asinformation relating to said logical unit information indicating thatthe information is composed over information storage areas in saidplurality of disk units and information storage areas in the otherplurality of disk units.
 13. A disk array unit according to claim 11,wherein said control unit performs power saving of the power supply ofsaid plurality of disk units by using a power saving mode forsuppressing power consumption by control of rotation of a spindle.
 14. Adisk array unit connected to a host unit to give information thereto andreceive information therefrom, said disk array unit comprising: aplurality of disk units for storing information transmitted from saidhost unit; a management information recording device, formed byutilizing information storage areas in the plurality of disk units, forcausing information relating to a logical unit for storing informationtransmitted from said host unit to correspond to information relating tothe plurality of disk units; and a control unit, when there is no accessfrom said host unit to said logical unit for a predetermined time, fordetermining said plurality of disk units corresponding to said logicalunit based on information recorded in said management informationrecording device and performing power saving of power supply for saidplurality of disk units, wherein said control unit further performing adiagnosis processing on said plurality of disk units being in the powersaving when another predetermined time has elapsed after start of thepower saving or at a specified time.
 15. A disk array unit according toclaim 14, further comprising: a plurality of logical units for saidplurality of disk units, wherein said control unit performs power savingof power supply for said determined plurality of disk units, when thereis no access from said host unit to any of said plurality of logicalunits for said predetermined time.
 16. A disk array unit according toclaim 14, wherein said logical unit is composed over information storageareas in said plurality of disk units and information storage areas inthe other plurality of disk units, and wherein said control unitperforms power saving of the power supply of said plurality of diskunits and power supply of said other plurality of disk units, when thereis no access from said host unit to said logical units for saidpredetermined time.
 17. A disk array unit according to claim 14, whereinsaid logical unit is composed over information storage areas in saidplurality of disk units and information storage areas in other pluralityof disk units, wherein said other plurality of disk units have aninformation storage area for constituting another logical unit, andwherein, when there is no the access from said host unit to said logicalunit for said predetermined time, said control unit performs the powersaving of the power supply of said plurality of disk units based oninformation recorded in said management information recording device, inconsideration of an access time from said host unit to said otherlogical unit, and performs the diagnosis on said plurality of disk unitsbeing in power saving.
 18. A disk array unit connected to a host unit togive information thereto and receive information therefrom, said diskarray unit comprising: a plurality of disk units for storing informationtransmitted from said host unit; a management information recordingdevice, formed by utilizing information storage areas in the pluralityof disk units, for causing information relating to a logical unit forstoring information transmitted from said host unit to correspond toinformation relating to the plurality of disk units; a control unit,when there is no access from said host unit to said logical unit for apredetermined time, for determining said plurality of disk unitscorresponding to said logical unit based on information recorded in saidmanagement information recording device and performing power saving ofpower supply for said determined plurality of disk units; and a port,connected with said control unit for receiving information relating tosaid predetermined time through a LAN or a RS232C connection of saidhost unit.
 19. A disk array unit according to claim 18, furthercomprising: a plurality of logical units for said plurality of diskunits, wherein said control unit performs power saving of power supplyfor said determined plurality of disk units, when there is no accessfrom said host unit to any of said plurality of logical units for saidpredetermined time.
 20. A disk array unit, according to claim 19,wherein said control unit performs a diagnosis on said plurality of diskunits being in the power saving when another predetermined time haselapsed after start of the power saving or at a specified time.
 21. Adisk array unit according to claim 20, wherein said port receivesinformation relating to said another predetermined time or saidspecified time through said LAN or said RS232C connection of said hostunit, and wherein said control unit receives the information relating tosaid another predetermined time or said specified time through saidport.
 22. A disk array unit according to claim 18, wherein said logicalunit is composed over information storage areas in said plurality ofdisk units and information storage areas in the other plurality of diskunits, and wherein said control unit performs power saving of the powersupply of said plurality of disk units and power supply of said otherplurality of disk units, when there is no access from said host unit tosaid logical units for said predetermined time.
 23. A disk array unitaccording to claim 22, wherein said control unit performs a diagnosis onsaid plurality of disk units and said other plurality of disk unitsbeing in the power saving when another predetermined time has elapsedafter start of the power saving or at a specified time.
 24. A disk arrayunit according to claim 23, wherein said port receives informationrelating to said another predetermined time or said specified timethrough said LAN or said RS232C connection of said host unit, andwherein said control unit receives the information relating to saidanother predetermined time or said specified time through said port. 25.A disk array unit according to claim 18, wherein said logical unit iscomposed over information storage areas in said plurality of disk unitsand information storage areas in other plurality of disk units, whereinsaid other plurality of disk units have an information storage area forconstituting another logical unit, and wherein, when there is no theaccess from said host unit to said logical unit for said predeterminedtime, said control unit performs the power saving of the power supply ofsaid plurality of disk units based on information recorded in saidmanagement information recording device, in consideration of an accesstime from said host unit to said other logical unit, and performs thediagnosis on said plurality of disk units being in power saving.
 26. Adisk array unit according to claim 25, wherein said control unitperforms a diagnosis on said plurality of disk units being in the powersaving when another predetermined time has elapsed after start of thepower saving or at a specified time.
 27. A disk array unit according toclaim 26, wherein said port receives information relating to saidanother predetermined time or said specified time through said LAN orsaid RS232C connection of said host unit, and wherein said control unitreceives the information relating to said another predetermined time orsaid specified time through said port.